[Comm2011] u flats / aux filter leakage

[Konrad Kuijken]

Pictures for Bernard, plus a quick note for the others:

In the u filter we have light leaking through the auxiliary filter onto the science array - quite a lot actually, up to 30% of the flux in nearby ccds is leakage.
The frames OMEGACAM_IMG_OBS214_FLAT0001 and 0002 (from 2011-08-02) are u dome flats. One is normal and in the other one the aux filter on one side was covered with a piece of paper. The difference between the two frames is the light leaking in through the aux filter.

Attached two pictures. The first is the flat field 1, obtained when the aux filter on the left is covered. The second is the difference between 2 and 1, ie the leaked light. Clearly it comes from the aux filter. The pattern is similar to the Jupiter experiment in comm2. 
Also notice the structure of the difference flat field: it does not show the regular pattern typical of u band flats, instead it is much flatter. This is all consistent with 'g' light leaking into the science ccds through the aux filter.

This is not nice - but on sky it will not be quite so bad since the sky is not as red as the dome flat lamps...
K


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